I think Evans' part will be just as small as it is in the book because Edgar Wright is known for putting in well-known actors in smaller parts (Cate Blanchett in a uncredited cameo in Hot Fuzz for example) so I am confident that star power won't take preference over the story.

anyone interested in Scott Pilgrimm's production should check out Edgar Wright's Myspace blog as he is posting 'a picture a day' charting the production of said film. just today there is some pics of his 'office' with a laptop, Scott Pilgrim books, photocopies of S.P art and various other things. He's in Canada now, so i figure we'll see some cool behind the scenes pics eventually as well.